I would have tried the 400, but my two best 400 grit hones, including the Chosera, are out on loan.
I suspect that the 400 might be pushing the limits!
I will say that there is a marked improvement in the shave from 600 to 800 to 1k. Also, even though you said that you got your three for knife work, all three are great for repair work on razors.